Dental casting alloy



, Patented June 13, i939 PATENT or ies DENTAL CASTING ALLOY Cornell .loel Grossman, Millburn, N. J.

No Drawing. Application April 25, 1939,

Serial No. 269,858

2 Claims. (Cl. 75-171) This invention relates to metallurgy and more particularly to an alloy suitable for use in the manufacture of cast dentures and the like.

In the manufacture of metallic dentures the 5 alloy composition employed must be stainless and 15 cast free from blow holes, voids and from slag and oxide inclusions, in a variety of irregular, shapesand configurations common to dentures with a minimum of material less and with a minimum of material surplus, by the ordinary g methods practiced in the art.

The present invention aims to provide an alloy adapted to meet these many conditions and further aims to provide a denture comprised of the said alloy.

55 The alloy composition of the present invention comprises a base consisting of nickel and cobalt in such relative proportions as to give the required strength, toughness and wear resistant properties desired and chromium in suificient ,0 amount to render the base stainless and corrosion resistant. Into this base I may incorporate manganese or silicon or both in such amounts as will be necessary to completely deoxidize the alloy and tocompletely neutralize 5 the deleterious effect of any sulfur or carbon present in the base and I may also incorporate a percentage of molybdenum or tungsten or both in such an amount as will augment the normal strength or rigidity of the base. Into the base or B into the base improved by additions of one or more of the metals manganese, silicon, molybdenum and tungsten, I incorporate a sufficient percentage of boron as will efiectively protect the alloy constituents from oxidation during subsequent re-melting and casting to form dentures.

In the manufacture of dentures it is customary in the art to melt the alloy in an open crucible by impinging thereon to open flame of an oxyacetylene or oxy-hydrogen blow torch. When I fully molten the alloy is centrifugally cast into a mold wherein relatively rapid solidification occurs. Heretofore in the art it has been diflicuh to manufacture cast dentures of metals other than the noble metals in this manner due to the fact that it is impractical to employ a protective slag over the metal during the melting and casting operation as the slag, when used, also entered the mold and was entrapped by the rapidly solidifying metal, causing blow holes, voids and the like. When, however, a protective slag was t not wed during the melting operation excessive oxidation of the metal constituents occurred and voids caused by oxide and gas occlusions are obtained. This circumstance has greatly limited the use and adaptation of chromium-containing 10 alloys, particularly in the forming of east dentures, due to the fact that when molten, or during melting the chromium content of such alloys rapidly oxidize to form difficultly fusible oxide compounds even though the alloy has been 16 covered or protected by readily fusible slag materials. 1

I have found that the most effective way to prevent the oxidation of the chromium in chromium-containing alloys is to incorporate in the alloy an alloy constituent which is more readily oxidizable than the chromium and which on oxidationforms a relatively low melting slag operating to protect the alloy from direct contact with oxidizing agents. Boron is the only alloy constituent of which I am aware that will accomplish this desired result. I

The amount of boron I may incorporate in the alloy composition of the present invention may vary widely without departure. I have successfully employed as low as 1.00% and as high as 10.00%. Under very expert manipulating conditions a boron content. or less than 1.0% probably can be employed but under the ordinary manipulating conditions of melting and casting I prefer to have present in my alloy about 5.0% boron, as this amount permits of repeated remelting without detrimental results to the alloy. The excess boron does not appear to be deleterious in the alloy but to the contrary appears to ill-- crease the fluidity the ease with which it may be cast, and cast dentures of my alloy containing 5% or more boron appear to be more sharply defined than those containing 1 or 2% boron. This amount of boron, moreover, appears to the physical properties'of the alloy, making it of finer grain structure and improving its hardness and luster.

Inmy alloy composition I prefer to limit any iron content to less than 1.00%. Iron in amounts greater than this, while being of advantage in some respects, such as giving added strength and ductility, detrimentally effect the corrosion resistance properties and require added chromium of the alloy when molten and beneficially adect in chromium within the ranges specified although this relation is} not empirical but solely for the purpose of maintaining relatively constant corrosion resistance properties in the alloy. Where molybdenum or tungsten or both are added to the alloy as stiffening constituents, I prefer to add these elements as'replacements for part of the cobalt and in this respect the cobalt, molybdenum and tungsten are to be considered to be substantial equivalents, although each in addition contribute to the corrosion resistant properties of the alloy. The molybdenum content may be as h gh as 8% but preferably should be in the range 2 to 4%. The tungsten content may be as high as 4% but preferably should be in the range 1 to As an example of the present invention, alloys that I have found most suitable for general purpose use in the casting of dentures have the following analyses:

Silicon.-

Alloys suitable for the same purpose but strongfor bridge work 'are simil but contain molybdenum 28% with the cobalt reduced a corresponding amount, or tungsten 1-4% with the cobalt reduced a corresponding amount.

Where a softer alloy is desired, as in the forming of pins, bars and the like which subsequently are to be best to shape, I increase the nickel to about 50% and lower the cobalt a corresponding amount, The boron content of this alloy operates to facilitate the subsequent weld attachment of these pins or bars to a cast denture and even er and more suitable lar to composition No.

permits;- the casting of the denture directly onto the pinjor bar as heretofore with other metals.

practiced in the art In the manufacture of the alloy composition of the present invention I prefer toseparately form a cobalt-nickel alloy, a chromium-nickel alloy, and a nickel-boron alloy or a nickel-chromiumboron alloy either of which alloys may contain manganese in such amounts as is necessary to effectively neutralize any sulfur present in the alloys. These alloys preferably should be substantially free from carbon and from iron. I then mix the various alloys together, preferably in small sized pieces, in such relative amounts as will give me the alloy composition desired, and melt the same down in an electric induction furnace under conditions protecting the metal from oxidation. When fully molten the alloy is cast in a mold adapted to form relatively small diameter rods which after solidification may be cut or broken into relatively small sized pieces. Where silicon, molybdenum or tungsten are to be added to the alloy, I preferably add them in the form of nickel alloys of these metals.

In the forming of a denture from this alloy, a sufficient amount of these small sized pieces of rod is placed in an open crucible and is melted by the direct application thereon of the oxy-acetylene or oXy-hydrogen flame and as soon as the metal becomes molten and fluid the molten metal is cast centrifugally into the denture mold as heretofore practiced in the art. The thus formed cast denture will be substantially free from blow holes, voids, or of oxide and slag inclusions. Any boron which is oxidized during the melting prior to casting forms such a fluid slag that on entering the mold during casting the same does not interfere with the entrance of the molten metal into the finest crevices of the mold, and a clearly defined sound casting will be obtained.

From the above description of the present invention, it will be apparent that the same may be widely varied as to alloy composition without departure from the invention and all such modification and variations are contemplated as may fall within the scope of the following claims:

What I claim is:

1. A dental casting alloy adapted to be repeatedly re-melted and cast into substantially sound cast dentures, said alloy comprising chromium 530%, cobalt 10-50%, manganese 1 to 2%, boron 1-10%, the balance of nickel.

2. A dental casting alloy adapted to be repeatedly re-melted and cast into substantially sound cast dentures, said alloy comprising chromium 25%, cobalt 36%, manganese 1%, boron 5%, the balance of the alloy consisting of nickel.

, CORNELL JOEL GROSSMAN.

the alloy consisting of- 

